In-Plane Field Type Liquid Crystal Display Device Comprising Liquid Crystal Molecules With More Than Two Kinds of Reorientation Directions

ABSTRACT

A liquid crystal display device includes a first substrate, a second substrate, a liquid crystal layer sandwiched between the first and second substrates, and an orientation film formed on the first substrate. The orientation film has two orientation regions in a pixel, and the orientation regions are formed by polarized light.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 12/649,582, filedDec. 20, 2009, which is a continuation of U.S. application Ser. No.12/046,873, filed Mar. 12, 2008, now U.S. Pat. No. 7,724,334, which is acontinuation of U.S. application Ser. No. 11/453,023, filed Jun. 15,2006, now U.S. Pat. No. 7,345,729, which is a continuation of U.S.application Ser. No. 10/400,448, filed Mar. 28, 2003, now U.S. Pat. No.7,158,202, which is a continuation of U.S. application Ser. No.10/237,756, filed Sep. 10, 2002, now U.S. Pat. No. 7,046,324, which is acontinuation of U.S. application Ser. No. 09/841,100, filed Apr. 25,2001, now U.S. Pat. No. 6,545,658, which is a continuation U.S.application Ser. No. 08/722,849, filed Sep. 26, 1996, now U.S. Pat. No.6,266,116, the subject matter of which is incorporated by referenceherein. This application also relates to U.S. Ser. No. ______ , filedconcurrently herewith and is also related to U.S. application Ser. No.10/637,495, filed Aug. 11, 2003, now U.S. Pat. No. 7,046,325, which isalso a continuation of U.S. application Ser. No. 10/400,448, now U.S.Pat. No. 7,158,202.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a liquid crystal display device and itsmanufacturing method, particularly to an art to be effectively appliedto an in-plane field type active-matrix liquid crystal display device.

(2) Description of the Prior Art

An active-matrix liquid crystal display device using an active elementsuch as thin film transistor (TFT) has been widely spread as a displayterminal of OA equipment because it is thin and lightweighted and has ahigh image quality equal to that of a cathode-ray tube.

The display system of the active-matrix liquid crystal display device isroughly divided into the following types.

One of them is a type, in which a liquid crystal layer is enclosedbetween a pair of substrates with two transparent electrodes formed onthe substrates, a driving voltage is applied to the transparentelectrodes, thereby driving the liquid crystal layer by an electricfield almost perpendicular to the surfaces of the substrates, and thelight passing the transparent electrodes and entering the liquid crystallayer is modulated (hereafter referred to as a vertical field type).Every product spread at present uses this type.

However, an active-matrix liquid crystal display device using thevertical field type has the problems on practical use that a contrast ofan image extremely varies when changing viewing angles and particularly,a gradation level is inverted depending on a viewing angle whendisplaying half tone images.

The other of them is a type, in which a liquid crystal layer is enclosedbetween a pair of substrates, a driving voltage is applied to twostripe-like or line-like electrodes formed on either or both of thesubstrates, thereby driving a liquid crystal layer by an electric fieldalmost parallel with the surfaces of the liquid crystal layer, and thelight entering the liquid crystal layer from the gap between the twoelectrodes is modulated (hereafter referred to as an in-plane fieldtype).

An active-matrix liquid crystal display device using the in-plane fieldtype can realize wide viewing-angle characteristics. However, anyactive-matrix liquid crystal display device using the in-plane fieldtype is not practically used yet.

Features of an active-matrix liqUid crystal display device using thein-plane field type are shown in the official gazettes of JapanesePatent Application No. 505247/1993, Japanese Patent Publication No.21907/1988, and Japanese Patent Laid-Open No. 160878/1994.

SUMMARY OF THE INVENTION

A conventional active-matrix liquid crystal display device using thein-plane field type modulates incoming light to a liquid crystal layerby rotating homogeneously initial-orienting liquid crystal moleculeswith no twisting, where an initial orientation direction is at aninclination to a pixel electrode and a counter electrode arranged inparallel, to create a reorientation state of liquid crystal moleculeswith twisting, whose major-axes are rotated substantially parallel withthe surfaces of the liquid crystal layer, and displays images by adriving voltage enough small for conventional video signal drivers andwith a response speed enough high to display animation.

Furthermore, the conventional active-matrix liquid crystal displaydevice using the in-plane field type has extremely wide viewing anglecharacteristics compared with the active-matrix liquid crystal displaydevice using the vertical field type.

However, the active-matrix liquid crystal display device using thein-plane field type cited above has a problem that viewing anglecharacteristics equal to those of a self-light-emitting display devicesuch as a cathode ray tube (CRT) cannot be achieved because ahomogeneous color tone cannot be realized and the viewing angle range ofisochromaticity narrows when tilting a viewing angle to a certaindirection.

That is, when liquid crystal molecules are twisted by rotation andviewing angle is tilted to the major-axis direction of the molecules,the birefringence anisotropy of the liquid crystal molecules more easilychanges compared with the case of tilting the viewing angle to otherdirections, so that gradation level is more easily inverted and colortone more easily changes in the major-axis direction than in otherdirections.

Particularly, when a white image is displayed in the normally blackmode, the color tone of white shifts to blue in the major-axis directionof the liquid crystal molecules.

Moreover, though the birefringence anisotropy does little change in theminor-axis direction of the liquid crystal molecules perpendicular tothe major-axis direction of them, the color tone of white shifts toyellow in the minor-axis direction because the optical path lengthincreases as the viewing angle tilts to the minor-axis direction.

The present invention has been made to solve the above mentionedproblems of the prior art and its object is to provide an art forrealizing wide viewing angle characteristics equal to those of a CRT andimproving the image quality for an active-matrix liquid crystal displaydevice using the in-plane field type.

The above and other objects and novel features of the present inventionwill become more apparent by the description of the presentspecification and the accompanying drawings.

The outline of a typical invention out of the inventions disclosed inthis application is briefly described below.

(1) An active-matrix liquid crystal display device comprises a pair ofsubstrates, a liquid crystal layer held between the substrates, aplurality of video signal lines formed on a first substrate of the pair,a plurality of scanning signal lines formed on the first substrate ofthe pair and intersecting the video signal lines, and a plurality ofpicture elements formed in a matrix in the intersecting regions betweenthe video signal lines and the scanning signal lines;

wherein each of the picture elements has at least an active elementformed on the first substrate, at least a pixel electrode connected tothe active element, and at least a counter electrode formed on either ofthe substrates to generate an electric field almost parallel with thesurfaces of the liquid crystal layer between the counter electrode andthe pixel electrode;

and wherein liquid crystal molecules of the liquid crystal layer have atleast two kinds of driving (reorientation) directions for neighboringpicture elements or in one picture element.

(2) For the means in the above Item (1), the liquid crystal molecules ofthe liquid crystal layer between the counter electrode and the pixelelectrode have one initial orientation direction.

(3) For the means in the above Item (2), each of the picture elementshas a plurality of pairs of pixel electrodes and counter electrodes;wherein each pair of a pixel electrode and a counter electrode have apair of facing sides faced almost parallel each other and the pluralityof pairs of the facing sides have a tilt angle to the initialorientation direction of the liquid crystal molecules.

(4) For the mean in the above Item (3), wherein the initial orientationdirection of the liquid crystal molecules is almost vertical to thescanning signal lines or parallel with the video signal lines, andpicture elements with tilt angles θ and −θ are alternately arranged intoa matrix.

(5) For the means in the above Item (4), the angle θ is kept in a rangeof 10°≦θ≦20°.

(6) For the means in the above Item (2), each of the picture elementshas a plurality of pairs of pixel electrodes and counter electrodes;wherein each pair of a pixel electrode and a counter electrode have apair of linear facing sides faced each other; and one of the pair oflinear facing sides has a tilt angle to the initial orientationdirection while the other of the pair is parallel with the initialorientation direction.

(7) For the means in the above Item (6), wherein the initial orientationdirection of liquid crystal molecules is almost vertical to the scanningsignal lines or parallel with the video signal lines, and the tiltangles of the plurality of pairs of facing sides are equal to θ and −θ.

(8) For the means in the above Item (7), the angle θ is kept in a rangeof 10°≦θ≦20°, and the numbers of the pairs of facing sides with tiltangles of θ and −θ in each of the picture elements are the same.

(9) For the means in the above Item (2), each of the picture elementshas a plurality of pairs of pixel electrodes and counter electrodes;wherein each pair of a pixel electrode and a counter electrode have apair of facing sides faced each other, and a first side of the pair isalmost parallel with the initial orientation direction while a secondside of the pair is formed by two parts, one part being extended almostparallel with the initial orientation direction and the other part beingtilted from the initial orientation direction at a tilt angle andintersecting with the first side at near the edge of the firstelectrode; and wherein the plurality of pairs of facing sides have aplurality of the tilt angles in each picture element.

(10) For the means in the above Item (9), wherein the initialorientation direction of liquid crystal molecules is almost vertical tothe scanning signal lines or almost parallel with the video signallines, and the plurality of the tilt angles are equal to θ and −θ.

(11) For the means in the above Item (10), the angle θ is kept in arange of 30°≦θ≦60°, and the numbers of the pairs of facing sides withthe tilt angles of θ and −θ in each of the picture elements are thesame.

(12) For the means in the above Item (2), each of the picture elementshas a plurality of pairs of pixel electrodes and counter electrodes;

wherein each pair of a pixel electrode and a counter electrode have apair of facing sides faced almost parallel each other and are bentinside the image display region of each of the picture elements.

(13) For the means in the above Item (12), wherein the video signallines or the scanning signal lines are bent to be almost parallel withthe pair of facing sides.

(14) For the means in the above Item (12), there are two or more typesof gap distances between pairs of pixel electrodes and counterelectrodes in each of the picture elements.

(15) For the means in the above Item (1), the liquid crystal moleculesof the liquid crystal layer between the counter electrode and the pixelelectrode have two initial orientation directions in each of the pictureelements.

(16) For the means in the above Item (15), the liquid crystal layer hasa positive dielectric anisotropy, initial orientation angles φLC1 andφLC2 are 90°+α and 90°−α, respectively, and angles φP1 and φP2 betweenthe transmission axes of two polarizing plates and the direction (EDR)ofthe applied electric field are 90° and 0° respectively.

(17) For the means in the above Item (15), the liquid crystal layer hasa negative dielectric anisotropy, initial orientation angles φLC1 andφLC2 are 0°+α and 180°−α, respectively, and angles φP1 and φP2 betweenthe transmission axes of two polarizing plates and the direction (EDR)of the applied electric field are 90° and 0°, respectively.

(18) For the means in the above Item (16) or (17), the absolute value ofa is 2.5° or less.

(19) For the means in the above Item (15), initial orientation anglesφLC1 and φLC2 are 45° and 135°, respectively, and angles φP1 and φP2between the transmission axes of two polarizing plates and the direction(EDR)of the applied electric field are 90° and 0° respectively.

(20) For the means in the above Item (15), the boundary between the twoinitial orientation directions of liquid crystal molecules is arrangedover a pixel electrode or a counter electrode in each of the pictureelements.

(21) For the means in the above Item (2) or (15), wherein an initialtwist angle of the liquid crystal layer is within 5 degrees of 0°.

(22) For a manufacturing method of an active-matrix liquid crystaldisplay device comprising a pair of substrates, a liquid crystal layerheld between the substrates, a plurality of active elements formed in amatrix on a first substrate of the pair, a plurality of pixel electrodesconnected to the active elements respectively, a plurality of counterelectrodes formed on either of the substrates to generate an electricfield almost parallel with the surfaces of the liquid crystal layerbetween the pixel electrodes and the counter electrodes, a pair oforientation films formed between the substrates and contacting theliquid crystal layer, and two polarizing plates formed on surfacesopposite to the surfaces of the substrates for holding the liquidcrystal layer; two-directional rubbings are applied to the bothorientation films in one picture element.

(23) For a manufacturing method of an active-matrix liquid crystaldisplay device comprising at least a pair of substrates, a liquidcrystal layer held between the substrates, a plurality of activeelements formed in a matrix on a first substrate of the pair, aplurality of pixel electrodes connected to the active elementsrespectively, a plurality of counter electrodes formed on either of thesubstrates to generate an electric field almost parallel with thesurfaces of the liquid crystal layer between the pixel electrodes andthe counter electrodes, a pair of orientation films formed between thesubstrates and contacting the liquid crystal layer, and two polarizingplates formed on surfaces opposite to the surfaces of the substrates forholding the liquid crystal layer; a chiral agent is mixed in the liquidcrystal layer and two-directional rubbings are applied only to either ofthe orientation films in one picture element.

(24) For a manufacturing method of an active-matrix liquid crystaldisplay device comprising at least a pair of substrates, a liquidcrystal layer held between the substrates, a plurality of activeelements formed in a matrix on a first substrate of the pair, aplurality of pixel electrodes connected to the active elementsrespectively, a plurality of counter electrodes formed on either of thesubstrates to generate an electric field almost parallel with thesubstrate surfaces to the liquid crystal layer between the pixelelectrodes and the counter electrodes, a pair of orientation filmsformed between the substrates and contacting the liquid crystal layer,and two polarizing plates formed on surfaces opposite to the surfaces ofthe substrates for holding the liquid crystal layer; two initialorientation directions of liquid crystal molecules are provided in onepicture element by applying a laser beam having two predeterminedpolarized directions to different regions of the orientation films inthe picture element.

According to the above means, shifts of color tones are offset eachother and the dependency of color-tone on a viewing angle can greatly bereduced because the initial orientation angle φLC is made different forneighboring picture elements or in one picture element so as to form twoor more kinds of reorientation directions.

For example, in an in-plane field type device utilizing the normallyblack mode, in which a displayed image is dark when no voltage isapplied and bright when a voltage is applied, and also utilizing thebirefringence first minimum mode, the transmission axes of the twopolarizing plates are perpendicularly intersected each other (crossNicols), and the maximum transmittance, that is, a white image isobtained when the angle formed between each transmission axis and themajor axis of liquid crystal molecules twisted by the electric fieldbecomes almost equal to 45□.

When changing viewing directions from an upward direction, which isvertical to the substrate surface, to a tilted direction toward thesubstrate surface in the major-axis direction of liquid crystalmolecules in the direction of about 45° away from the transmission axisunder the above twisted state, the birefringence anisotropy changes andthe color tone of white shifts to blue in the major-axis direction.

In the minor-axis direction of liquid crystal molecules (at a directionof about −45° away from the transmission axis, and perpendicular to themajor-axis direction), the birefringence anisotropy does little changeby tilting viewing angles from a vertical direction to an in-planedirection.

However, the color tone of white shifts to yellow in the minor-axisdirection because the optical path length increases as the viewing angletilts from a vertical to a in-plane direction in the minor-axisdirection.

The important point is that, because blue and yellow colors arecomplimentary colors in chromaticity coordinates, white color can becreated by mixing these two colors.

Therefore, by rotating liquid crystal molecules in two directions foreach picture element or in one picture element, and by creating tworeorientation states where the major-axis directions of the two statesare nearly perpendicular to each other in displaying a white image or ahalf-tone image, color tones of the two states are offset each other andthe viewing angle dependency of color tone change can greatly bereduced.

Moreover, also for gradation inversion, the characteristics of both theminor-axis direction of liquid crystal molecules to be hardlygradation-reversed and the major-axis direction of them to be easilygradation-reversed are averaged and the no-inversion viewing angle rangeof a gradation level can be expanded.

Thereby, the homogeneity of gradation and that of color tone areaveraged or expanded in every direction and wide viewing anglecharacteristics close to those of a CRT can be realized.

The foregoing and other objects, advantages, manner of operation andnovel features of the present invention will be understood from thefollowing detailed description when read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an essential portion showing one picture elementand its neighborhood of the active-matrix color liquid crystal displaydevice which is embodiment 1 of the present invention;

FIGS. 2A to 2D are illustrations showing the directions (EDR) of appliedelectric field, the initial orientation direction (RDR), transmissionaxes directions (OD1 and OD2) of polarizing plates (POL1 and POL2), anddriving directions of liquid crystal molecules (LC) of the liquidcrystal display device of embodiment 1 of the present invention;

FIG. 3 is an illustration showing an example of arranging the pictureelement shown in FIG. 1 or a similar picture element into a matrix;

FIG. 4 is a top view showing one picture element and its neighborhood ofthe active-matrix color liquid crystal display device of embodiment 2 ofthe present invention;

FIGS. 5A and 5B are illustrations showing the directions (EDR) ofapplied electric field, the initial orientation direction (RDR),transmission axes directions (OD1 and OD2) of polarizing plates (POL1and POL2), and driving directions of liquid crystal molecules (LC) ofthe liquid crystal display device which is embodiment 2 of the presentinvention;

FIG. 6 is an illustration showing an example of arranging the pictureelement shown in FIG. 4 or a similar picture element into a matrix;

FIG. 7 is a top view showing one picture element and its neighborhood ofthe active-matrix color liquid crystal display device which isembodiment 3 of the present invention;

FIGS. 8A and 8B are illustrations showing the directions (EDR) ofapplied electric field, the initial orientation direction (RDR),transmission axes directions (OD1 and OD2) of polarizing plates (POL1and POL2), and driving directions of liquid crystal molecules (LC) ofthe liquid crystal display device of embodiment 3 of the presentinvention;

FIG. 9 is an illustration showing an example of arranging the pictureelement shown in FIG. 7 and a similar picture element into a matrix;

FIG. 10 is an illustration showing an example of arranging the pictureelement shown in FIG. 7 and a similar picture element into a matrix;

FIG. 11 is a top view showing one picture element and its neighborhoodof the active-matrix color liquid crystal display device which isembodiment 4 of the present invention;

FIGS. 12A and 12B are illustrations showing the directions (EDR) ofapplied electric field, the initial orientation direction (RDR),transmission axes directions (OD1 and OD2) of polarizing plates (POL1and POL2), and driving directions of liquid crystal molecules (LC) ofthe liquid crystal display device of embodiment 4 of the presentinvention;

FIG. 13 is an illustration showing an example of arranging the pictureelement shown in FIG. 7 or a similar picture element into a matrix;

FIG. 14 is an illustration showing one picture element and itsneighborhood of the active-matrix color liquid crystal display devicewhich is embodiment 5 of the present invention;

FIGS. 15A and 15B are illustrations showing the directions (EDR) ofapplied electric field, the initial orientation direction (RDR),transmission axes directions (OD1 and OD2) of polarizing plates (POL1and POL2), and driving directions of liquid crystal molecules (LC) ofthe liquid crystal display device of embodiment 5 of the presentinvention;

FIG. 16 is a top view showing one picture element and its neighborhoodof the active-matrix color liquid crystal display device which isembodiment 6 of the present invention;

FIGS. 17A, 17B, and 17C are illustrations showing the directions (EDR)of applied electric field, the initial orientation direction (RDR),transmission axes directions (OD1 and OD2) of polarizing plates (POL1and POL2), and driving directions of liquid crystal molecules (LC) ofthe liquid crystal display device of embodiment 6 of the presentinvention;

FIG. 18 is a top view of an unit picture element of example 1 in theliquid crystal display device of embodiment 7 of the present invention;

FIG. 19 is a top view of an unit picture element of example 2 in theliquid crystal display device of embodiment 7 of the present invention;

FIG. 20 is a top view of an unit picture element of example 4 in, theliquid crystal display device of embodiment 7 of the present invention;

FIG. 21 is a top view of an unit picture element of example 5 in theliquid crystal display device of embodiment 7 of the present invention;

FIG. 22 is a top view of an unit picture element of example 6 in theliquid crystal display device of embodiment 7 of the present invention;

FIG. 23 is a top view showing one picture element and its neighborhoodof the active-matrix color liquid crystal display device of embodiment 8of the present invention;

FIG. 24 is a top view showing one picture element and its neighborhoodof the active-matrix color liquid crystal display device of embodiment11 of the present invention;

FIG. 25 is an illustration showing a method for rubbing a bottomorientation film (ORI1) of the active-matrix color liquid crystaldisplay device of embodiment 8 of the present invention;

FIG. 26 is an illustration showing a method for applying a laser beamhaving two predetermined polarized directions to different regions of abottom orientation film (ORI1) of the active-matrix color liquid crystaldisplay device of embodiment 13 of the present invention;

FIGS. 27A and 27B are graphs showing the azimuthal angle (φ) dependentcharacteristics of white color tone when driving the liquid crystaldisplay device of the present invention.and the liquid crystal displaydevice of the comparative example, in which FIG. 27A shows the case ofthe comparative example and FIG. 27B shows the case of the presentinvention.

FIGS. 28A and 28B show a color tone constant region (an isochromaticregion) in the form of semispherical polar-coordinate (θ,φ) graphs, inwhich FIG. 28A shows the case of the comparative example and FIG. 28Bshows the case of the present invention and both of which showdistributions of the white color tone.

FIG. 29 is an illustration showing the relation between the directions(EDR) of the applied electric field, initial orientation directions(RDR1 and RDR2), and polarized-light transmission axes (OD1 and OD2).

FIG. 30 is an illustration showing the definition of the viewing angle(θ, φ) of each embodiment of the present invention;

FIG. 31 is a sectional view of the picture element in FIG. 1, takenalong the line a-a in FIG. 1;

FIG. 32 is a sectional view of the thin film transistor (TFT) in FIG. 1,taken along the line 4-4 in FIG. 1;

FIG. 33 is a sectional view of the storage capacitance (Cstg) in FIG. 1,taken along the line 5-5 in FIG. 1;

FIG. 34 is a top view for explaining the structure of portions aroundthe matrix of the display panel (PNL) of the liquid crystal displaydevice of each embodiment of the present invention;

FIG. 35 is a sectional view showing the margin of a panel havingscanning signal terminals at its left side and having no externalconnection terminals at its right side in the liquid crystal displaydevice of each embodiment of the present invention;

FIG. 36 is a flow chart of sectional views of a thin film transistorelement portion and a gate terminal portion showing the manufacturingprocess of steps A to C at the transparent substrate (SUB1) of theliquid crystal display device of each embodiment of the presentinvention;

FIG. 37 is a flow chart of sectional views of a thin film transistorelement portion and a gate terminal portion showing the manufacturingprocess of steps D to F at the transparent substrate (SUB1) of theliquid crystal display device of each embodiment of the presentinvention;

FIG. 38 is a flow chart of sectional views of a thin film transistorelement portion and a gate terminal portion showing the manufacturingprocess of steps G to H at the transparent substrate (SUB1) of theliquid crystal display device of each embodiment of the presentinvention;

FIG. 39 is an illustration showing the equivalent circuit and itsperipheral circuits of the display matrix portion (AR) of the liquidcrystal display device of each embodiment of the present invention;

FIG. 40 is an illustration showing driving waveforms of the liquidcrystal display device of each embodiment of the present invention atdriving;

FIG. 41 is a top view showing the state in which peripheral drivingcircuits are mounted on the liquid crystal panel of each embodiment ofthe present invention; and

FIG. 42 is an exploded perspective view of a liquid crystal module ofthe liquid crystal display device of each embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below in detail byreferring to the accompanying drawings.

In all drawings for explaining embodiments of the invention, componentshaving the same function are provided with the same symbol andrepetitive description of them is omitted.

[Embodiment 1]

First, the in-plane field type active-matrix color liquid crystaldisplay device constituted in accordance with embodiment 1 of thepresent invention is outlined below.

<<Planar structure of matrix portion (picture element portion)>>

FIG. 1 is a top view showing one picture element and its neighborhood ofthe active-matrix color liquid crystal display device of embodiment 1 ofan invention of the present invention.

Each picture element is arranged in a region (a region enclosed by foursignal lines) where two adjacent scanning signal lines (gate signallines or horizontal signal lines)(GL) and two adjacent video signallines (drain signal lines or vertical signal lines)(DL) intersect.

Each picture element includes thin film transistor (TFT), storagecapacitance (Cstg), a pixel electrode (PX), two counter electrodes (CT),and a counter voltage signal line (a common signal line) (CL).

In FIG. 1, a plurality of scanning signal lines (GL) and a plurality ofcounter voltage signal lines (CL) are arranged in the vertical directionwhile extending in the horizontal direction.

Moreover, a plurality of video signal lines (DL) are arranged in thehorizontal direction while extending in the vertical direction.

Furthermore, a pixel electrode (PX) is connected to a source electrode(SD1) of a thin film transistor (TFT) and two counter electrodes (CT)are integrated with a counter voltage signal line (CL).

A pixel electrode (PX) and each of two counter electrodes (CT) are facedeach other, controlling optical states of liquid crystal layer (LCD) byan electric field between the pixel electrode (PX) and the counterelectrode (CT).

The pixel electrode (PX) and the two counter electrodes (CT) are formedlike comb teeth. As shown in FIG. 1, the pixel electrode (PX) extendsstraight diagonally downward, and the two counter electrodes (CT) areformed in a comb tooth shape which protrude upward from a countervoltage signal line (CL) and whose facing sides faced with the pixelelectrode (PX) also extend diagonally upward. The region between thepixel electrode (PX) and the two counter electrodes (CT) is divided intotwo parts in one picture element.

Sectional structure of display matrix portion (picture elementportion)>>

FIG. 31 is a sectional view showing the essential portion in FIG. 1,taken along the line 31 a-31 a in FIG. 1. FIG. 32 is a sectional viewshowing thin film transistor (TFT) in FIG. 1, taken along the line 4-4in FIG. 1. FIG. 33 is a sectional view showing a storage capacitance(Cstg) in FIG. 1, taken along the line 5-5 in FIG. 1.

As shown in FIGS. 31 to 35, thin film transistors (TFT), storagecapacitances (Cstg), and electrodes group are formed at the bottomtransparent glass substrate (SUB1) side, and color filter (FIL) andlight shielding black matrix (BM) are formed at the top transparentglass substrate (SUB2) side.

Moreover, orientation films (OR1 and ORI2) for controlling initialorientation directions of liquid crystal molecules (LC) at the surfacesof the liquid crystal layer are provided between transparent glasssubstrates (SUB1 and SUB2), and polarizing plates (POL1 and POL2) areprovided on the outside surfaces of each of transparent glass substrates(SUB1 and SUB2).

More minute structures are described below.

<<TFT substrate>>

First, the structure of the bottom transparent glass substrate (SUB1)(TFT substrate) is described below in detail.

<<Thin film transistor (TFT)>>

Thin film transistor (TFT) operates so that the channel resistancebetween the source and drain decreases by applying a positive bias tothe gate electrode and increases by decresing the bias to zero.

As shown in FIG. 32, thin film transistor (TFT) comprises gate electrode(GT), gate insulating film (GI), i-type semiconductor layer (AS) made ofi-type (intrinsic, or undoped) amorphous silicon (Si), and a pair of asource electrode (SD1), and a drain electrode (SD2).

A source electrode (SD1) and a drain electrode (SD2) are originallydetermined by the bias polarity between them. Because the polarity ofthe circuit of the present liquid crystal display device is invertedduring operation, a source electrode (SD1) and a drain electrode (SD2)are replaced each other during operation.

In the following description, however, one is fixed to source electrode(SD1) and the other is fixed to drain electrode (SD2) for conveniencesake.

The embodiment of the present invention uses an amorphous-silicon thinfilm transistor as thin film transistor (TFT). However, it is alsopossible to use a two-terminal device such as a polysilicon thin filmtransistor, MOS transistor on a silicon wafer, organic TFT, or MIM(Metal-Insulator-Metal) diode (though each of them is not strictly anactive element, it is assumed as an active element in the case of thepresent invention).

<<Counter electrode (CT)>>

Counter electrode (CT) is made of conductive film (g1) on the same layeras gate electrode (GT) and scanning signal line (GL).

Moreover, anodic oxide film (AOF) made of aluminum oxide is formed oncounter electrode (CT).

Counter electrode (CT) is constituted so that counter voltage (Vcon)) isapplied to counter electrode (CT).

<<Counter voltage signal line (CL>>

Counter voltage signal line (CL) is made of conductive film (gl).

Counter voltage signal line (CL) is formed in the same manufacturingprocess as that of conductive films (g1) of gate electrode (GT),scanning signal line (GL), and counter electrode (CT).

Counter voltage (Vcom) is supplied to counter electrode (CT) from anexternal circuit through counter voltage signal, line (CL).

Moreover, anodic oxide film (AOF) made of aluminum oxide is formed oncounter voltage signal line (CL).

Furthermore, it is possible to form counter electrode (CT) and countervoltage signal line (CL) at the top transparent-glass substrate(SUB2)(color filter substrate) side.

<<Insulating film (G1)>>

Insulating film (GI) is used as a gate insulating film for providing anelectric field for semiconductor layer (AS) together with gate electrode(GT) in thin film transistor (TFT).

Insulating film (GI) is formed over gate electrode (GT) and scanningsignal line (GL). Insulating film (GI) uses, for example, a siliconnitride film formed by plasma CVD and is formed at a thickness of 1,200to 2,700 A (approx. 2,400 A for the embodiment of the presentinvention).

Gate insulating film (GI) is formed so as to entirely enclose displayMatrix portion (AR) and its margin is removed so that external terminals(DTM and GTM) are exposed.

Insulating film (GI) also contributes to electrical insulation betweencounter voltage signal line (CL) and video signal line (DL).

<<Pixel electrode (PX)>>

Pixel electrode (PX) comprises conductive film (dl), and conductive film(d2) formed on conductive film (dl).

Moreover, pixel electrode (PX) is formed on the same layer as sourceelectrode (SD1) and drain electrode (SD2). Furthermore, pixel electrode(PX) is integrated with source electrode (SD1).

<<Storage capacitance (Cstg)>>

Pixel electrode (PX) is constituted so as to overlap with countervoltage signal line (CL) at the end opposite to the end connected withthin film transistor (TFT).

As shown in FIG. 33, this overlap constitutes storage capacitance (Cstg)using pixel electrode (PX) as one electrode (PL2) and counter voltagesignal (CL) as other electrode (PL1).

The dielectric film of storage capacitance (Cstg) comprises insulatingfilm (GI) used as a gate insulating film of thin film transistor (TFT)and anodic oxide film (AOF).

As shown in FIG. 1, planar storage capacitance (Cstg) is arranged on apart of conductive film (gl) of a counter voltage signal line (CL).

<<Color filter substrate>>

Then, the structure of the top transparent-glass substrate (SUB2) (colorfilter substrate) is described in detail below by referring to FIGS. 1and 31.

<<Light shielding film (BM)>>

Light shielding film (BM) (so-called black matrix) is formed at the toptransparent glass substrate (SUB2) side so that contrast of a displayedimage is not deteriorated due to the light transmitted through anunnecessary gap other than the gap between a pixel electrode (PX) and acounter electrode

(CT) and emitted to the display surface side.

Light shielding film (BM) also has a function for preventing externallight or backlight from entering semiconductor layer (AS).

That is, i-type semiconductor layer (AS) of thin film transistor (TFT)is sandwiched between light shielding film (BM) and slightly-large gateelectrode (GT) from the top and bottom and thereby protected fromexternal natural light or backlight.

The inside of the closed polygonal contour of light shielding film (BM)shown in FIG. 1 shows an opening where light shielding film (BM) is notformed.

Light shielding film (BM) has a shielding characteristic to light and ismade of a film with a high insulating property not so as to influencethe electric field between a pixel electrode (PX) and a counterelectrode (CT). For the embodiment of the present invention, lightshielding film (BM) uses a mixture obtained by mixing black pigment withresist and formed at a thickness of approx. 1.2 μm.

Light shielding film (BM) is formed like a lattice around each pictureelement and the lattice partitions the effective display region of onepicture element.

Therefore, the contour of each picture element is made clear by lightshielding film (BM).

That is, light shielding film (BM) has a function for serving as a blackmatrix and a function for shielding light to i-type semiconductor layer(AS).

Light shielding film (B) is also formed on the margin like a frame andits pattern is formed continuously with the pattern of the matrixportion provided with a plurality of dot-like openings shown in FIG. 1.

Light shielding film (BM) at the margin is extended to the outside ofsealing portion (SL) to prevent leak light such as reflected light dueto a real machine such as a personal computer from entering the displaymatrix portion.

Moreover, light shielding film (BM) is kept in a range approx. 0.3 to1.0 mm inside from the peripheral edge of top transparent-glasssubstrate (SUB2) and formed so as to avoid the cutting region of toptransparent-glass substrate (SUB2).

<<Color filter (FIL)>>

Color filter (FIL) is formed like a stripe in repetition of red, green,and blue and moreover, it is formed so as to overlap with the edge oflight shielding film (BM).

Color filter (FIL) can be formed as shown below.

First, a dyeing base material such as an acrylic resin is formed on thesurface of top transparent-glass substrate (SUB2) and then the dyeingbase material other than that in a red-filter forming region is removedby photolithography. Thereafter, the dyeing base material is dyed by ared dye and fixed to form red filter (R).

Then, green filter (G) and blue filter (B) are successively formed bythe same process.

<<Overcoat film (OC)>>

Overcoat film (OC) is used to prevent a dye from leaking from colorfilter (FIL) to a liquid crystal layer and flatten steps due to colorfilter (FIL) and light shielding film (BM).

Overcoat film (OC) is made of, for example, a transparent resin such asacrylic resin or epoxy resin.

<<Structure around display matrix portion (AR)>>

FIG. 34 is an illustration showing a top view of an essential portionaround display matrix (AR) portion of display panel (PNL) including topand bottom transparent-glass substrates (SUB1 and SUB2).

FIG. 35 is an illustration showing the cross section of the neighborhoodof external connection terminal (GTM) to which a scanning circuit shouldbe connected at the left side and the cross section of the neighborhoodof a sealing portion free from external connection terminal at the rightside.

Terminal groups (Tg and Td) are named by collecting every severalscanning-circuit connection terminals (GTM), video-signal-circuitconnection terminals (DTM), and their outgoing wiring portions forconnection with tape carrier packages (TCP).

Counter electrode terminal (CTM) is a terminal for supplying countervoltage (Vcom) to counter electrode (CT) from an external circuit.

Counter voltage signal line (CL) of the display matrix portion isextended to the opposite side (right side in drawings) toscanning-circuit terminal (GTM), and counter voltage signal lines (CL)are collected by common bus line (CB)(counter electrode connectionsignal line) and connected to counter electrode terminal (CTM).

Layers of orientation films (ORI1 and ORI2) are formed inside of sealingpattern (SL) and polarizing plates (POL1 and POL2) are formed on theoutside surfaces of bottom transparent glass substrate (SUB1) and toptransparent glass substrate (SUB2), respectively.

Liquid crystal layer (LCD) is sealed in a region partitioned by sealingpattern (SL) between bottom orientation film (ORI1) and top orientationfilm (ORI2) for setting the orientation of liquid crystal molecules.

Bottom orientation film (ORI1) is formed on protective coat (PSV) overthe bottom transparent-glass substrate (SUB1).

The liquid crystal display device of each embodiment of the presentinvention is fabricated by superposing various layers to separately formbottom transparent glass substrate (SUB1) and top transparent glasssubstrate (SUB2), thereafter forming sealing pattern (SL) on the toptransparent glass substrate (SUB2), superposing top transparent glasssubstrate (SUB2) on bottom transparent glass substrate (SUBI) and,injecting liquid crystal (LCD) through opening portion (INJ) of sealingpattern (SL), sealing injection port (INJ) with epoxy resin or the like,and cutting the top and bottom substrates.

<<Equivalent circuit of whole display device>>

FIG. 39 is a connection diagram of an equivalent circuit of displaymatrix portion (AR) and its peripheral circuits.

In FIG. 39, symbol AR denotes a display matrix portion (matrix array) inwhich a plurality of picture elements are two-dimensionally arranged.

In FIG. 39, symbol PX denotes a pixel electrode, in which additionalcharacters G and B are added correspondingly to green and bluerespectively. Symbols y0, y1, . . . , and yend of scanning signal line(GL) denote the sequence of scanning timing.

Scanning signal line (GL) is connected to vertical scanning circuit (V)and video signal line (DL) is connected to video signal driving circuit(H). Circuit (SUP) includes a power supply circuit for obtaining aplurality of stabilized voltage sources of divided voltages obtainedfrom one voltage source and a circuit for converting the information foran CRT (cathode ray tube) sent from a host (host arithmetic processingunit) to the information for a (TFT) liquid crystal display device.

<<Driving method>>

FIG. 40 is an illustration showing driving waveforms when driving theliquid crystal display device of the embodiment of the presentinvention. V_(G)(i-1) and V_(G)(i) denote the gate voltages (scanningsignal voltages) applied to the (i-1)-th and (i)-th scanning signallines (GL) respectively.

Moreover, V_(D)(j) denotes a video signal voltage applied to videosignal line (DL) and Vc denotes counter voltage (Vcom) applied tocounter electrode (CT).

Furthermore, Vs(i,j) denotes a pixel electrode voltage applied to pixelelectrode (PX) of the picture element at row (i) and column (j) andV_(LC)(i,j) denotes a voltage applied to a liquid crystal layer of thepicture element at row (i) and column (j).

The method for driving the liquid crystal display device of eachembodiment of the present invention converts counter voltage (Vcom)applied to counter electrode (CT) to two AC rectangular waves of VCH andVCL as shown by Vc and changes non-selective voltages of gate voltage(VG) applied to gate electrode (GT) in two values of VGLH and VGLL foreach scanning period synchronously with the AC rectangular waves.

In this case, the amplitude of counter voltage (Vcom) is made equal tothat of non-selective voltages of gate voltage (VG).

Video signal voltage (VD) applied to video signal line (DL) is equal tovoltage (VSIG) obtained by subtracting ½ of the amplitude of countervoltage (VC) from a voltage to be applied to a liquid crystal layer.

DC voltage, instead of AC voltage, can be used for counter voltage(Vcom) to be applied to counter electrode (CT). However, by using AC forcounter voltage (Vcom), the maximum amplitude of video signal voltage(VD) can be reduced and a circuit with a low withstand voltage can beused for the video signal driving circuit (signal-side driver).

<<Functions of storage capacitance (Cstg)>>

Storage capacitance (Cstg) is used to store the video informationwritten in picture elements for a long time after thin film transistor(TFT) is turned off.

In the case of an in-plane field type device, which is used for eachembodiment of the present invention, video information cannot be storedin picture elements unless there is storage capacitance (Cstg) because aliquid crystal capacitance (Cpix) constituted between a pixel electrode(PX) and a counter electrode (CX) is so smaller than a capacitance(Cpix) of a vertical field type device that this capacitance (Cpix) canbe hardly worked as a holding capacitance.

Therefore, storage capacitance (Cstg) is an indispensable component forthe in-plane field type device.

Moreover, storage capacitance (Cstg) operates so as to decreaseinfluences of gate potential change OVG) on pixel electrode potential(Vs) when thin film transistor (TFT) is switched.

This state is shown by an expression below.

ΔVs={Cgs/(Cgs+Cstg+Cpix)}XΔVG  [Mathematical expression 1]

In the above expression, Cgs denotes a parasitic capacitance formedbetween gate electrode (GT) and source electrode (SD1) of thin filmtransistor (TFT), Cpix denotes a capacitance formed between pixelelectrode (PX) and counter electrode (CT), and ΔVs denotes a change of apixel electrode potential due to ΔVG, that is, a so-called feed-throughvoltage.

Though the above change (ΔVs) is a cause of a DC component added to aliquid crystal layer, it can be decreased by increasing holdingcapacitance (Cstg).

Decrease of the DC component applied to liquid crystal layer (LCD) makesit possible to improve the life time of liquid crystal layer (LCD) andreduce the so-called sticking in which a latent image is left on aliquid crystal display screen.

As described above, because gate electrode (GT) is increased in size soas to cover i-type semiconductor layer (AS), the region overlapped withsource electrode (SD1) and drain electrode (SD2) increases by theincreased region of electrode (GT) and therefore, the disadvantagesoccur that parasitic capacitance (Cgs) increases and pixel electrodepotential (Vs) is effected by gate voltage (scanning signalvoltage)(VG).

However, by using storage capkitance (Cstg), the disadvantages can besettled.

<<Manufacturing method>>

Then, a method for manufacturing the bottom transparent-glass substrate(SUB1) side of the liquid crystal display device described above isexplained below by referring to FIGS. 36 to 38.

In FIGS. 36 to 38, characters at the center show abbreviations of stepnames, the left side shows the thin film transistor (TFT) portion shownin FIG. 32, and the right side shows the processing flow of sectionalshapes nearby a gate terminal.

Steps A to I are classified correspondingly to each photographicprocessing except steps B and D. Any sectional view of each step shows astage in which processing after photographic treatment is completed andphotoresist is removed.

In the following description, photographic treatment is defined as aseries of operations from application of photoresist to selectiveexposure using a mask and development of it and repetitive descriptionis avoided.

Description is made below in accordance with classified steps.

(Step A, FIG. 36)

Conductive film (gl) with a thickness of 3,000 Å comprisingaluminum(Al)-palladium(Pd), alunninum(Al)-silicon(Si),aluminunn(Al)-tantalum(Ta), or aluminum(Al)-titanium(Ti)-tantalum(Ta) isformed on bottom transparent-glass substrate (SUB1) by sputtering.

After photographic treatment, conductive film (gl) is selectively etchedby a mixed acid solution of phosphoric acid, nitric acid, glacial aceticacid, and water.

Thereby, anodic oxide bus line (SHg) (not illustrated) for connectinggate electrode (GT), scanning signal line (GL), counter electrode (CT),counter voltage signal line (CL), electrode (PL1), first conductive filmof common bus line (CB), first conductive film of counter electrodeterminal (CTM), and gate terminal (GTM) and anodic oxide pad (notillustrated) connected to anodic oxide bus line (SHg) are formed.

(Step B, FIG. 36)

Anodic oxide mask (AO) is formed by direct drawing and thereafter,bottom transparent-glass substrate (SUB1) is soaked in an anodic oxidesolution obtained by diluting a solution which is obtained by preparing3% tartaric acid with ammonia to PH of 6.25±0.05 with an ethylene glycolsolution to 1:9 to make adjustment so that a formation-current densitycomes to 0.5 mA/cm² (constant current formation).

Then, anodizing is performed until a formation voltage of 125 V isreached which is necessary to obtain aluminum oxide film (AOF) with apredetermined thickness.

Thereafter, it is preferable to keep aluminum oxide film (AOF) under theabove state for tens of minutes (constant voltage formation).

This is important to obtain homcigeneous aluminum oxide film (AOF).Thereby, conductive film (gl) is anode-oxidized and anodic oxide film(AOF) with a thickness of 1,800 A is formed on gate electrode (GT),scanning signal line (GL), counter electrode (CT), counter voltagesignal line (CL), and electrode (PL1).

(Step C, FIG. 36)

Transparent conductive film (g2) made of an ITO film with a thickness of1,400 Å is formed by sputtering.

After photographic treatment, transparent conductive film (g2) isselectively etched by a mixed acid solution of hydrochloric acid andnitric acid as an etching solution to form the highest layer of gateterminal (GTM), drain terminal (DTM), and the second conductive film ofcounter electrode terminal (CTM).

(Step D, FIG. 37)

Ammonia gas, silane gas, and nitrogen gas are introduced into a plasmaCVD system to form a silicon nitride film (SiNx) with a thickness of2,200 Å and moreover, silane gas and hydrogen gas are introduced intothe plasma CVD system to form an i-type amorphous silicon (Si) film witha thickness of 2,000 Å. Thereafter, hydrogen gas and phosphine gas areintroduced into the plasma CVD system to form N(+)-type amorphoussilicon (Si) film with a thickness of 300 Å.

(Step E, FIG. 37)

After photographic treatment, i-type semiconductor pattern (AS) isformed by using carbon tetrachloride (CC1 ₄) and sulfur hexafluoride(SF₆) as dry etching gases and thereby selectively etching an N(+)-typeamorphous silicon (Si) film and i-type amorphous silicon (Si) film.

(Step F, FIG. 37)

After photographic treatment, a silicon nitride film is selectivelyetched by using sulfur hexafluoride (SF₆) as a dry etching gas.

(Step G, FIG. 38)

Conductive film (d1) made of chromium (Cr) with a thickness of 600 Å isformed by sputtering and moreover, conductive film (d2) comprisingaluminum(Al)-tantalum(Ta) or aluminum(Al)-titanium(Ti)-tantalum(Ta) witha thickness of 4,000 Å is formed by sputtering.

After photographic treatment, conductive film (d2) is etched by a mixedacid solution of phosphoric acid, nitric acid, glacial acetic acid, andwater and conductive film (dl) is etched by a cerium(II) nitrate ammoniasolution to form video signal line (DL), source electrode (SD1), drainelectrode (SD2), pixel electrode (PX), electrode (PL2), second and thirdconductive films of common bus line (CB), and bus line (SHd) forshorting drain terminal (DTM) (not illustrated).

The resist used for the embodiment of the present invention usessemiconductor resist OFPR800(trade name) made by TOKYO OHKA KOGYO CO.,LTD.

Then, N(+)-type semiconductor layer (d0) between the source and drain isselectively removed by introducing carbon tetrachloride (CC1 ₄) andsulfur hexafluoride (SF₆) into a dry etching system and thereby etchingan N(+)-type amorphous silicon (Si) film.

(Step H, FIG. 38)

Ammonia gas, silane gas, and nitrogen gas are introduced into a plasmaCVD system to form a silicon nitride film with a thickness of 1 μm.

After photographic treatment, protective coat (PSV) is formed byselective etching the silicon nitride film by the photolithography usingsulfur hexafluoride (SF₆) as a dry etching gas.

<<Display panel (PNL) and driving-circuit substrate PCB1>>

FIG. 41 is a top view showing a state in which video-signal drivingcircuit (H) and vertical scanning circuit (V) are connected to displaypanel (PNL) shown in FIG. 34 and the like.

In FIG. 41, CHI denotes a driving IC chip for driving display panel(PNL). Five driving IC chips of the vertical scanning circuit side areshown at the bottom of FIG. 41 and ten driving IC chips of thevideo-signal driving circuit side are shown at the left of FIG. 41.

TCP denotes a tape carrier package on which driving, IC chip (CHI) ismounted by tape automated boding (TAB) and PCB1 denotes a drivingcircuit substrate with tape carrier package (TCP) and capacitorsmounted. PCBL is divided into a video-signal driving circuit portion anda scanning-signal driving circuit portion.

FGP denotes a frame ground pad to which a spring-shaped fragment cutdeep into shield case (SHD) is soldered.

FC denotes a flat cable for electrically connecting bottomdriving-circuit substrate (PCB1) with left driving-circuit substrate(PCB1).

Flat cable (FC) uses a cable obtained by sandwiching and supporting aplurality of lead wires obtained by plating phosphor bronze wires withtin (Sn)} by striped polyethylene layer and polyvinyl alcohol layer.

<<General structure of liquid crystal display module (MDL)>>

FIG. 42 is an exploded perspective view showing each components ofliquid crystal display module (MDL).

SHD denotes a frame-like shield case made of a metallic plate (metalframe), LCW denotes a display window of the case, PNL denotes a liquidcrystal display panel, SPB denotes a light diffusing plate, LCB denotesa light guiding body, RM denotes a reflector, BL denotes a backlightfluorescent tube, and LCA denotes a backlight case. Module MDL isfabricated by superposing various members according to the verticalarrangement shown in FIG. 42.

The whole of module (MDL) is secured by pawls and hooks provided forshield case (SHD).

Backlight case (LCA) is formed So as to house backlight fluorescent tube(BL), light diffusing plate (SPB), light guiding body (LCB), andreflector (RM), which changes the light emitted from backlightfluorescent tube (BL) arranged at the side of light guiding body (LCB)to homogeneous backlight on the display surface by light guiding body(LCB), reflector (RM), and light diffusing plate (SPB) and emits thehomogeneous backlight toward liquid crystal panel (PNL).

Backlight fluorescent tube (BL) connects with inverter substrate (PCB3)which serves as a power supply of tube (BL).

<<Liquid crystal layer and polarizing plate>>

Then, a liquid crystal layer, orientation films, and polarizing platesare described below.

<<Liquid crystal layer>>

Liquid crystal layer (LCD) uses nematic liquid crystal with a positivedielectric anisotropy Δε of 13.2 and a refractive index anisotropy Δn of0.081 (589 nm, 20°C.).

The thickness (gap) of the liquid crystal layer is set to 3.9 μm and theretardation Δn×d is set to 0.316.

The value of the retardation Δn×d is set so as to be half of theapproximately average wavelength of the wavelength characteristic ofbacklight and so that the color tone of the transmitted light of theliquid crystal layer becomes white © light source, chromaticitycoordinates x=0.3101, y=0.3163).

In other words, this value of the fetardation Δn×d is set to a so-calledfirst minimum mode of birefringence effect.

When the angle between the polarized-light transmission axis of apolarizing plate and the major-axis direction of liquid crystalmolecules is equal to about 45□, the maximum transmittance can beobtained and transmitted light hardly having waveform dependency in arange of visible light can be obtained.

The thickness (gap) of the liquid crystal layer is controlled by polymerbeads.

Moreover, as the dielectric anisotropy Δε increases, a driving voltagecan be lowered. Furthermore, as the refractive index anisotropy Δndecreases, it is possible to increase the thickness (gap) of the liquidcrystal layer, shorten the liquid-crystal sealing time, and decrease gapfluctuation.

<<Orientation film>>

Orientation films (ORI1, ORI2) are made from polyimide.

In the case of rubbing method, rubbing directions of orientation filmsdetermine initial orientation directions (RDR) of liquid crystalmolecules (LC) at both surfaces of a liquid crystal layer.

In embodiment 1 of the present invention, orientation films (ORI1, ORI2)are rubbed in parallel or anti-parallel directions with each other.

Moreover, in the embodiment 1, orientation films (ORI1, ORI2) are rubbedin parallel with video signal lines (DL) or vertical to scanning signallines (GL), as shown in FIG. 1.

There are two kinds of initial arrangements of liquid crystal moleculesbetween orientation films (ORI1, ORI2) when no voltage is appliedbetween the electrodes (PX) and (CX).

The first kind of initial arrangement is formed by rubbing orientationfilms (ORI1, ORI2) in the same (parallel) directions so that tilt anglesare distributed in such a form that liquid crystal molecules around thecenter of the liquid layer have almost zero tilt angles, while liquidcrystal molecules at the near surface of the liquid crystal layer have atilt angle almost equal to a pretilt angle.

This arrangement of molecules is called a splay state, and is suitableto attain wide viewing characteristics because the molecules near thetop and bottom surfaces of the liquid crystal layer work to compensatetheir optical characteristics each other.

The second kind of initial arrangement is formed by rubbing orientationfilms (ORI1, ORI2) in the anti-parallel directions, that means a rubbingdirection of bottom orientation film (ORI1) is opposite to a rubbingdirection of top orientation film (ORI2), so that tilt angles aredistributed, in such a form that almost all liquid crystal moleculesbetween orientation films (ORI1, ORI2) are tilted in parallel by anangle almost equal to a pretilt angle.

The second arrangement of molecules is called a parallel state.

In this specification, if not specified, the first initial arrangement asplay state is formed as an initial state, but the second initialarrangement (a parallel state) is also applicable to the presentinvention.

Especially, for embodiment 6 described later, a parallel state is moresuitable to create two driving directions easily and uniformly.

<<Direction (EDR) of applied electric field >>

In this specification, a direction (EDR) of an applied electric field isdefined as the direction of a component parallel with the surfaces of aliquid crystal layer between a pixel electrode (PX) and a counterelectrode (CX) of an applied electric field in a gap between a pixelelectrode (PX) and a counter electrode (CX).

In the case of line or stripe electrodes, the direction (EDR) is thedirection perpendicular to the extended directions of the electrodes(PX) and (CX).

<<Initial orientation angle φLC >>

In this specification, an initial orientation direction RDR is definedas the direction parallel with a surface of a liquid crystal layerbetween a pixel electrode (PX) and a counter electrode (CX), of aninitial direction of major axes of liquid crystal molecules at thesurface of the liquid crystal layer.

More specifically, an initial orientation direction RDR is defined as arubbing direction or an opposite direction of the rubbing direction.

And, in this specification, an initial orientation angle φLC is definedas the angle of an initial orientation direction RDR from a direction(EDR) of an applied electric field, is positive when an initialorientation direction RDR rotates counter-clockwise from the direction(EDR) of an applied electric field, and is defined in the range of0°≦LC<180° as shown in FIG. 29.

<<Initial twist angle >>

In each embodiments of the present invention, the initial orientationangles φLC-b on a bottom orientation film ORI1 side and φLC-t on a toporientation film ORI2 side are set to almost the same value so thatliquid crystal molecules are free from twisting when no voltage isapplied between the electrodes (PX) and (CX).

For convenience sake, φLC means the same angles of φLC-b and φLC-t, andφLC is only shown in the figures.

However, a twist angle within 5 degrees of zero degrees, or | φLC-φLC-t| ≦5°, is also applied to each embodiment of this invention in order toshift a driving voltage range to a more suitable range, or to improvecontrast of a image in a fixed driving voltage range.

<<Polarizing plate>>

FIGS. 2A to 2D are illustrations showing the directions of the appliedelectric field of the liquid crystal display device of the embodiment 1of the present invention, the directions of polarized-light transmissionaxes (OD1 and OD2) of polarizing plates (POL1 and POL2), and drivingdirections of liquid crystal molecules (LC).

As shown in FIG. 2C, the polarized-light transmission axis (OD1) ofbottom polarizing plate (POL1) and polarized-light transmission axis(0D2) of polarizing plate (POL2) are perpendicular to each other and thedirection of either polarized-light transmission axis (OD1) or (OD2) ismade parallel with initial orientation direction (RDR) of liquid crystallayer.

Thereby, the embodiment 1 of the present invention makes it possible toobtain the characteristic of the normally black mode.

Also, the normally white mode in which the transmittance decreases asthe voltage applied to a picture element increases can be obtained bymaking the directions of polarized-light transmission axis (OD1) andpolarized-light transmission axis (OD2) parallel with the initialorientation direction (RDR).

As shown in FIG. 1, in the case of the embodiment 1 of the presentinvention, the facing sides of a pixel electrode (PX) and two counterelectrodes (CT) are tilted from initial orientation direction (RDR) soas to be tilted by a tilt angle of θ(or −θ).

For each embodiment in this specification, a tilt angle of θ is definedas a tilt angle of a facing side from initial orientation direction(RDR), and is positive when a facing side is tilted counter-clockwisefrom initial orientation direction (RDR).

Thereby, the initial orientation angle φLC is set to 90°−θ so that thedriving direction of liquid crystal molecules (LC) in the liquid crystaldriving region, which is a region formed between a counter electrode(CT) and a pixel electrode (PX), is determined as a clockwise rotationas shown in FIG. 2D.

The embodiment of the present invention makes it possible to decrease adriving voltage and increase a response speed by arranging the driving(reorientation) directions of liquid crystal molecules to a singlereorientation direction in the liquid crystal driving region.

FIG. 3 is an illustration showing an example of arranging the pictureelement shown in FIG. 1 or similar picture element into a matrix.

The embodiment 1 of the present invention makes it possible to vary thedriving direction of liquid crystal molecules (LC) to clockwise or tocounter-clockwise rotation by forming picture elements including counterelectrodes (CT) and pixel electrodes (PX) whose facing sides have a tiltangle of θ or −θ to initial orientation direction (RDR) and arrangingthem into a matrix as shown in FIG. 3.

Thereby, the embodiment 1 of the present invention makes it possible tocompensate the heterogeneity of white color tone due to a viewing anglecaused by a unified driving direction in homogeneously-oriented liquidcrystal layer (LCD), improve the display quality, and obtain ahigh-quality display image.

It is most suitable to set a tilt angle θ between 10° and 20° tocompensate optical characteristics in the major axis and in the minoraxis.

FIG. 3 shows an example of alternately arranging picture elementsincluding counter electrodes (CT) and pixel electrodes (PX) whose facingsides have a tilt angle of θ or −θ to initial orientation direction(RDR), which is parallel with video signal line (DL) or vertical toscanning signal line (GL).

Because the driving direction of liquid crystal molecules (LC) differsin adjacent picture elements, it is possible to improve the opticalcompensation effect for the heterogeneity of white color tone due to aviewing angle.

The embodiment 1 of the present invention makes it possible tocompletely homogenize the white color tone in a range up to 50° of φ inevery direction of θ in the viewing angle (θ, φ) defined in FIG. 30.

[Embodiment 2]

FIG. 4 is a top view showing one picture element and its neighborhood ofthe active-matrix color liquid crystal display device of embodiment 2 ofthe present invention.

FIGS. 5A and 5B are illustrations showing the directions (EDR) ofapplied electric fields, the directions of polarized-light transmissionaxes (OD1 and OD2) of polarizing plates (POL1 and POL2), and drivingdirections of liquid crystal molecules (LC) in the liquid crystaldisplay device of the embodiment 2 of the present invention. Thestructure of the embodiment 2 of the present invention is the same asthat of embodiment 1 of the present invention except the shapes of apixel electrode (PX) and two counter electrodes (CT).

In the case of the embodiment 2 of the present invention, as shown inFIG. 4, a pixel electrode (PX) forms an approximately triangular shapeextending diagonally downward, two counter electrodes (CT) protrudingupward from a counter voltage signal line (CL) form a comb tooth shapeextending diagonally upward, and the region between a pixel electrode(PX) and two counter electrodes (CT) is divided into two parts in onepicture element. In the case of the embodiment 2 of the presentinvention, rubbing directions of liquid crystal molecules (LC) at topand bottom orientation films sides are parallel each other and alsoparallel with video signal lines (DL) or vertical to scanning signallines (GL) as shown in FIG. 4.

Moreover, in the case of the embodiment 2 of the present invention, thefacing sides of pixel electrodes (PX) and counter electrodes (CT) aretilted as shown in FIG. 4 so that they are tilted by an angle of θ forone pair of facing sides and −θ for the other pair of facing sides inone picture element.

Thereby, the initial orientation angles φLC are set to 90°−θ and 90° +θin one picture element so that the driving directions of liquid crystalmolecules (LC) are fixed to a clockwise rotation and a counter-clockwiserotation, respectively, as shown in FIG. 5B.

Therefore, the embodiment 2 of the present invention makes it possibleto use two driving directions of liquid crystal molecules (LC) in onepicture element so that this embodiment is possible to further improvethe compensation effect for the heterogeneity of white color tone due toa viewing angle.

Further, it is desirable to set a tilt angle θ between 10° and 20° tocompensate optical characteristics more effectively.

The arrangement shown in FIG. 6 is an example of arranging the pictureelement shown in FIG. 4 into a matrix.

[Embodiment 3]

FIG. 7 is a top view showing one picture element and its neighborhood ofthe active-matrix cold liquid crystal display device of embodiment 3 ofthe present invention.

FIGS. 8A and 8B are illustrations showing the directions (EDR) ofapplied electric field, the directions of polarized-light transmissionaxes (OD1 and OD2) of polarizing plates (POL1 and POL2), and drivingdirections of liquid crystal molecules (LC).

The structure of the embodiment 3 of the present invention is the sameas that of embodiment 1 of the present invention except the shapes oftwo pixel electrodes (PX) and three counter electrodes (CT).

In the case of the embodiment 3 of the present invention, as shown inFIG. 7, two pixel electrode (PX) are tilted inside an opening region oflight shielding film (BM) of one picture element and formed into a Vshape, three counter electrodes (CT) form a comb tooth shape protrudingupward from a counter voltage signal line (CL), and the region betweentwo pixel electrodes (PX) and three counter electrodes (CT) is dividedinto four parts in one picture element.

In the case of the embodiment 3 of the present invention, the rubbingdirections of the orientation films, that is, initial orientationdirections (RDR) are parallel each other at top and bottom surfaces ofthe liquid crystal layer and moreover parallel with video signal lines(DL) or vertical to scanning signal lines (GL), as shown in FIG. 7.

Moreover, three counter electrodes (CT) are parallel with initialorientation direction (RDR) and two pixel electrodes (PX) are tilted toform a zigzag shape so that each pixel electrode (PX) is tilted by anangle of θ or −θ from initial orientation direction (RDR).

Thereby, the initial orientation angles φLC near facing sides of pixelelectrodes (PX) are set to 90°−θ and 90° +θ, in one picture element sothat the driving directions of liquid crystal molecules (LC) are fixedto a clockwise rotation and a counter-clockwise rotation, respectively,as shown in FIG. 8B.

Therefore, the embodiment 3 of the present invention makes it possibleto use two driving direction of liquid crystal molecules (LC) in onepicture element.

Further, it is desirable to set tilt angle θ between 10° and 20° tocompensate optical characteristics more effectively.

FIGS. 9 and 10 are illustrations showing examples of arranging thepicture element shown in FIG. 7 into a matrix.

FIG. 9 shows an example of arranging the picture element shown in FIG. 7into a matrix and FIG. 10 shows an example of alternately arranging thepicture element shown in FIG. 7 and a picture element symmetric to thepicture element in FIG. 7 for the direction of scanning signal line (GL)into a matrix in the direction parallel with video signal line (DL)while sharing counter voltage signal line (CL) by two picture elements.

In the case of the arrangement shown in FIG. 10, it is possible tofurther improve the heterogeneity due to the viewing angle of whitecolor tone because the driving direction of liquid crystal molecules(LC) differs not only in one picture element but also in adjacentpicture elements along video signal line.

Moreover, it is possible to increase the display region per pictureelement compared with the cases of the above embodiments 1 and 2 of thepresent invention and display a brighter image with lower powerconsumption.

[Embodiment 4]

FIG. 11 is a top view showing one picture element and its neighborhoodof the active-matrix color liquid crystal display device of embodiment 4of the present invention.

FIGS. 12A and 12B are the directions of the applied electric field, thedirections of polarized-light transmission axes (OD1 and 0D2), anddriving directions of liquid crystal molecules (LC) in the liquidcrystal display device of the embodiment 4 of the present invention.

The structure of the embodiment 4 of the present invention is the sameas that of embodiment 1 of the present invention except the shapes of apixel electrode (PX) and two counter electrodes (CT).

In the case of the embodiment 4 of the present invention, as shown inFIG. 11, a pixel electrode (PX) extends straight downward, two counterelectrodes (CT) form a comb tooth shape which protrudes upward from acounter voltage signal line (CL) and the region between a pixelelectrode (PX) and two counter electrodes (CT) is divided into two partsin one picture element.

Moreover, in the case of the embodiment 4 of the present invention, asshown in portion A in FIG. 11, each of two counter electrodes (CT)inside the portion A is tapered.

Thereby, a counter electrode (CT) and a pixel electrode (PX) areintersected each other at an angle of θ or −θ through an insulating film(GI).

The distance between a counter electrode (CT) and a pixel electrode (PX)is narrowed at the intersecting portion and the strongest electric fieldis applied to the tapered region.

Therefore, when a voltage is applied between the electrodes (PX) and(CX), liquid crystal molecules (LC) of liquid crystal layer (LCD) at theintersecting portion are first driven.

Thereby, liquid crystal molecules (LC) in the liquid crystal drivingregion between a counter electrode (CT) and a pixel electrode (PX) inthe image display region are influenced by the initial driving directionof liquid crystal molecules (LC) at the intersection portion and drivenin the same direction as liquid crystal molecules (LC) at theintersecting portion.

Therefore, in the case of the embodiment 4 of the present invention, thedriving direction of liquid crystal molecules (LC) is determined by theintersecting angle.

That is, in the embodiment 4 of the present invention, two intersectingangles formed between two counter electrode (CT) and a pixel electrode(PX) are set to θ and −θ, as shown in FIG. 12B.

Therefore, the embodiment 4 of the present invention also makes itpossible to use two driving direction of liquid crystal molecules (LC)in one picture element.

Though it is possible to set angle θ greater than zero degrees butsmaller than 90 degrees, it is most preferable to set the angle θbetween 30° and 60°.

FIG. 13 is an illustration showing a case of arranging the pictureelement in FIG. 11 into a matrix.

Moreover, in the case of the embodiment 4 of the present invention, apixel electrode (PX) and two counter electrodes (CT) are formed inparallel with the rubbing directions of orientation films (ORI1, ORI2).

Therefore, when rubbing the orientation films, it is possible tosmoothly apply a buffing cloth to the sides of each electrode in apicture element display region so that the orientation of liquid crystalmolecules at the sides of the electrode can be improved to preventdomains from appearing.

[Embodiment 5]

FIG. 14 is a top view showing one picture element and its neighborhoodof the active-matrix liquid crystal display device of embodiment 5 ofthe present invention.

FIGS. 15A and 15B are illustrations showing the directions of theapplied electric field, the directions of polarized-light transmissionaxes (OD1 and OD2) of polarizing plates (POL1 and POL2), and drivingdirections of liquid crystal molecules (LC) of the liquid crystaldisplay device of the embodiment 5 of the present invention.

The structure of the embodiment 5 of the present invention is the sameas that of embodiment 1 of the present invention except the shapes of apixel electrode (PX) and two counter electrodes (CT).

In the case of the embodiment 5 of the present invention, as shown inFIG. 14, a pixel electrode (PX) extends straight downward in the imagedisplay region, two counter electrodes (CT) have a comb tooth shapeprotruding upward from a counter voltage signal line (CL), and theregion between a pixel electrode (PX) and two counter electrodes (CT) isdivided into two parts in one picture element.

In the case of the embodiment 5 of the present invention, as shown inportion A in FIG. 14, a pixel electrode (PX) inside the portion A isformed into a trapezoid, and two counter electrodes (CT) and a pixelelectrode (PX) are intersected each other at angles of θ and −θ throughan insulating film (GI) inside a portion A and outside of the imagedisplay region.

Also, in the case of the embodiment 5 of the present invention, thedriving directions of liquid crystal molecules (LC) are determined bythe intersecting portion as shown in FIG. 15B.

That is, in the case of embodiment 4, the initial driving directions ofliquid crystal molecules (LC) are determined by two counter electrodes(CT) tilted from a linear pixel electrode (PX).

In the case of the embodiment 5, however, the initial driving directionsof liquid crystal molecules (LC) are determined by a pixel electrode(PX) tilted from two linear counter electrodes (CT).

Therefore, the embodiment 5 of the present invention also makes itpossible to use two driving direction of liquid crystal molecules (LC)in one picture element.

Though it is possible to set angle θ greater than zero degrees butsmaller than 90 degrees, it is most preferable to set the angle θbetween 30° and 60°.

In the case of the embodiment 5 of the present invention, the rubbingdirections of orientation films are parallel each other and moreoverparallel with video signal line (DL) or vertical to scanning signal line(GL), as shown in FIG. 14.

[Embodiment 6]

FIG. 16 is a top view showing one picture element and its neighborhoodof the active-matrix liquid crystal display device of embodiment 6 ofthe present invention.

FIGS. 17A to 17C are illustrations showing the directions (EDR) ofapplied electric field, the directions of polarized-light transmissionaxes (OD1 and OD2) of polarizing plates (POL1 and POL2), and drivingdirections of liquid crystal molecules (LC) of the active-matrix colorliquid crystal display device of the embodiment 6 of the presentinvention. The embodiment 6 of the present invention is the same as theembodiment 1 except the following structures.

In the case of the embodiment 6 of the present invention, as shown inFIGS. 17A and 17B, a top orientation film (OR12), a protective coat(PSVI), counter voltage signal lines (CL) and counter electrodes (CT),an overcoat film (OC), color filter (FIL), and light shielding blackmatrix (BM) are formed over the top transparent-glass substrate (SUB2).

Moreover, a storage capacitance (Cstg) is constituted by superposing oneend of a pixel electrode (PX) and a scanning gate line (GL) at theforward or next scanning stage through an insulating film (GI).

In the case of the embodiment 6 of the present invention, the rubbingdirections of orientation films are parallel each other and moreoverparallel with counter electrodes (CT), pixel electrodes (PX), and videosignal lines (DL), or vertical to scanning signal lines (GL), as shownin FIG. 16.

Moreover, counter voltage signal lines (CL) and counter electrodes (CT)are arranged on a top transparent-glass substrate (SUB2) and, as shownin FIG. 17B, an electric field between a pixel electrode (PX) and acounter electrode (CT) is formed to be slightly tilted from thesubstrate.

In this case, the driving direction of liquid crystal molecules isdetermined by a first angle between a direction of a slightly tiltedelectrical field and a pretilt direction of liquid crystal molecules(LC) at bottom surface of a liquid crystal layer in a portion close topixel electrode (PX), and by a second angle between a direction of aslightly tilted electrical field and a pretilt direction of liquidcrystal molecules (LC) in a portion close to counter electrode (CT), asshown in FIG. 17C.

To match the first and second angles more effectively the rubbingdirections of orientation films (ORI1, ORI2) are selected to establish aparallel molecules arrangement. However, a so-called splay moleculesarrangement is also applicable to this embodiment.

In the case of the embodiment 6 of the present invention, as shown inFIG. 17B, counter electrodes (CT) formed on a top transparent-glasssubstrate (SUB2) and pixel electrodes (PX) formed on a bottomtransparent-glass substrate (SUB1) are alternately arranged.

Therefore, tilting directions of electrical fields between the counterelectrodes (CT) and pixel electrodes (PX) from the substrate areopposite each other in the liquid crystal driving region.

Therefore, in the embodiment 6 of the present invention, two differentdriving directions are created in one picture element.

Also in the case of the embodiment 6 of the present invention, rubbingis smoothly and securely performed nearby sides of an electrode in theimage display region when rubbing an orientation film.

Therefore, it is possible to improve the orientation of liquid crystalmolecules of a liquid crystal layer at the sides of an electrode.

[Embodiment 7]

FIG. 18 shows a schematic view of an liquid crystal display device ofembodiment 7 of the present invention. When a pixel electrode PX and twocounter electrodes CT have a bent structure or zigzag shape as shown inFIG. 18, two electric field directions EDR are generated in one pictureelement.

Liquid crystal molecules arranged along parallel rubbing directions aredifferent in their rotational directions due to two electric fielddirections (EDR) and a single initial orientation direction (RDR) ofliquid crystal molecules LC when a voltage is applied between theelectrodes PX and CT.

Moreover, the liquid crystal display device can be manufactured bymaking a pixel electrode unparallel with a counter electrode.

Though the angle of a bent portion is not restricted, it is morepreferable to set the angle in a range not less than 120° but less than180° because the bend of a picture element is not observed by the nakedeye.

If the angle formed between an electrode and a rubbing direction is toosmall, a problem occurs that a multipli-gradation display cannot be madebecause the voltage-transmittance characteristic of a liquid crystaldevice becomes extremely steep. This problem can be solved by settingtwo or more different inter-electrode distances in one picture element.

Threshold voltages of the voltage-transmittance characteristics of thisembodiment can be changed in accordance with inter-electrode distancesso-that the voltage-transmittance characteristics of one picture elementare averaged under the two or more gap distances, becomes gradual, and,thereby, multiple-gradation display can be made.

Moreover, when using the structure in which only a pixel electrode and acounter electrode are bent as shown in FIG. 18, a region between a videosignal line and a counter electrode increases and the opening ratiodecreases.

This problem can be solved by also forming the video signal line orscanning signal line into an analogous bent structure.

[Example 1]

In the case of this embodiment, both angles of the bent portions of thepixel electrodes and counter electrodes are set to 170° as shown in FIG.18.

The gap distance between a pixel electrode and a counter electrode isthe same in all picture element and it is set to 30 μm.

Rubbing directions on top and bottom orientation films sides are almostparallel each other and also vertical to scanning signal lines.

The polarized-light transmission- axis of one polarizing plate is madealmost parallel with the rubbing direction and that of the otherpolarizing plate is made perpendicular to the rubbing direction.Thereby, the normally black mode is obtained.

Viewing angle characteristics of the panel thus manufactured areevaluated within ±60° of φ by using an inspection apparatus (Model C5718made by HAMAMATSU PHOTONICS Co., Ltd.).

By displaying images of eight gradations and measuring the viewing angledependency of brightness at each gradation, no tone reversal occurred inthe manufactured panel at any angle within ±60° of φ.

[Example 2]

FIG. 19 is an illustration showing another example of this embodiment inthe unit picture element.

The liquid crystal display device is manufactured similarly to example 1except that shapes of two pixel electrode and three counter electrodesare changed as shown in FIG. 19 and the gap distance between pixelelectrodes and counter electrodes is changed to 15 μm.

As the result of measuring viewing angle characteristics similarly tothe ease of example 1, no tone reversal occurred at any angle within±60° of φ.

[Example 3]

The liquid crystal display device is manufactured similarly to example 2except that angles of the bent portions of pixel electrodes and counterelectrodes are changed to 178°.

As the result of measuring viewing angle characteristics similarly tothe case of example 1, no tone reversal occurred at any angle within ±60of φ.

As the result of measuring a voltage at which the transmittance ismaximized and a voltage at which the transmittance is equal to 1% of themaximum transmittance, voltages of 2.5 V and 1.5 V are obtainedrespectively. The difference between the voltages is 1.0 V, which isremarkably small.

[Example 4]

FIG. 20 is an illustration showing example 4 of this embodiment in onepicture element.

The liquid crystal display device is manufactured similarly to example 3except that two types of gap distances of 20 μm and 10 μm are formedbetween pixel electrodes and counter electrodes in one picture element.

As the result of measuring viewing angle characteristics similarly toexample 1, no tone reversal occurred at any angle within ±60° of φ.

As the result of measuring a voltage at which the transmittance ismaximized and a voltage at which the transmittance is equal to 1% of themaximum transmittance, voltages of 3.4 V and 1.0 V are obtained,respectively. The difference between the voltages is 2.4 V, which islarge and suitable for displaying multiple gradation levels.

[Example 5]

FIG. 21 is an illustration showing example 5 of this embodiment in onepicture element.

The liquid crystal display device is manufactured similarly to example 2except that an electrode has a structure in which a driving directiondiffers at right-hand side and left-hand side as shown in FIG. 21 andthe initial orientation direction of liquid crystal molecules isparallel with scanning signal lines.

The same result of viewing angle characteristics as example 1 has beenobtained.

[Example 6]

FIG. 22 is an illustration showing example 6 of this embodiment in theunit picture element.

The liquid crystal display device is manufactured similarly to example 2except that two pixel electrodes are not parallel with three counterelectrodes as shown in FIG. 22 and the angle formed between theelectrodes is 5°.

The same result of viewing angle characteristics as example 1 has beenobtained.

[Embodiment 8]

In the case of the embodiment 8 of the present invention, the steps offorming a thin film transistor and electrodes are the same as those ofembodiment 1 of the present invention.

<<Initial orientation direction>>

In the embodiment 8 of the present invention, initial orientationdirections (φLC1 and φLC2) of liquid crystal molecules are controlled byrubbing top orientation film (OR12) and bottom orientation film (ORI1)so that rubbings are performed in two directions (φLC1 and φLC2) foreach picture element.

FIG. 23 shows divided rubbing regions, in which region 501 and region502 are rubbed in different directions (RDR1 and RDR2), respectively.

FIG. 25 is an illustration showing a method for rubbing bottomorientation film (ORI1) in the embodiment 8 of the present invention.

As shown in FIG. 25, because two initial orientation directions areprovided for liquid crystal molecules at the surfaces of a liquidcrystal layer in one picture element, the whole surface of bottomorientation film (ORI1) is rubbed in the RDR1 direction and thereafter,rubbed again in the RDR2 direction in the photoresist process by maskingthe surface with resist (RES).

Portions not masked with resist (RES) are re-rubbed in the RDR2direction.

Thereafter, rubbings can be performed in two directions by removingresist (RES) from the surface.

The process of rubbings in FIG. 25 is also applied to top orientationfilm (ORI2) in each direction so that the rubbing directions for bothtransparent-glass substrates (SUB1 and SUB2) are almost parallel eachother.

FIG. 29 is an illustration showing the relation between the direction(EDR) of the applied electric field, initial orientation directions(RDR1 and RDR2), and polarized-light transmission axes (OD1 and OD2).

In FIG. 29, φLC1 and φLC2 show the initial orientation angles formedbetween the direction of the applied electric field (EDR) and initialorientation directions (RDR1 and RDR2) in regions 501 and 502.

In the case of the embodiment of the present invention, LC1 is set to75° and φLC2 is set to 105□.

The initial orientation angles φLC1 and φLC2 must be kept between 45°and 90° (90° excluded) and between 90° and 135° (90° excluded),respectively, when dielectric anisotropy Δε of a liquid crystal ispositive, while the initial orientation angles φLC1 and φLC2 must bekept between 0° and 45° (0° excluded) and between 145° and 180° (180°excluded), respectively, when the dielectric anisotropy Δε is negative.

Therefore, when liquid crystal with a negative dielectric anisotropy isused for the embodiment 8 of the present invention, it is necessary toset φLC1 to 15° and φLC2 to 165°.

<<Polarizing plate>>

As shown in FIG. 29, the angle φP1 is set to 90° and the angle φP2 isset perpendicular to it so that φP2 is equal to 0°.

Thereby, it is possible to obtain the normally black mode.

[Comparative example]

The liquid crystal display device of the comparative example is the sameas embodiment 8 except the fact of only one direction of φLC1=φLC2=75□,φP1=75° and φP2=165°.

FIGS. 27A and 27B are graphs showing the azimuthal angle (φ) dependentcharacteristics of white color tone when driving the liquid crystaldisplay device of the embodiment 8 of the present invention and theliquid crystal display device of the comparative example, in which FIG.27A shows the case of the comparative example and FIG. 27B shows thecase of the embodiment 8 of the present invention.

X-coordinate and y-coordinate are chromaticity coordinates according tothe CIE1931 X-Y-coordinate system.

These are measured at four azimuthal angles θ defined in FIG. 30 whichare 0°, 40°, 90°, and 150°.

Moreover, a symbol θ denotes an aximuthal angle of a viewing directionin its circumferential direction parallel with the panel surface, and asymbol θ denotes a polar angle of a viewing direction from the directionvertical to the panel surface.

From the results of the comparative example shown in FIG. 27A, it isfound that the white color tone greatly differs depending on a viewingangle.

In the case of the embodiment Of the present invention shown in FIG.27B, however, it is found that the white color tone hardly changes.

This is because rotation angles of liquid crystal molecules in tworubbing regions are symmetric with respect to a line normal to thedirection of electric field application and thereby, there is an effectof offsetting coloring each other and it is possible to further expandthe angular range in which the white color tone is constant.

Therefore, according to the embodiment 8 of the present invention, it isfound that complete color tone constancy can be realized in a range upto ±50° of φ in the whole circumferential direction θ.

FIGS. 28A and 28B show the color tone constancy (the isochromaticregion) in the form of semispherical polar-coordinate (θ, φ) graphs, inwhich FIG. 28A shows the case of the comparative example and FIG. 28Bshows the case of the embodiment 8 of the present invention and both ofwhich show distributions of the white color tone.

The expression of “color shift of 1 ΔC unit” is used for the embodimentof the present invention as an expedient scale for deciding a shift of acolor tone.

When X and Y coordinates of the white color tone are shifted from thefront white color tone up to +0.02 or more, the shift is defined as“color shift of 1 ΔC unit (shift to yellow)”.

When the coordinates are shifted up to −0.02 or more, the shift isdefined as “color shift of 1 ΔC unit (shift to blue)”.

In the case of the comparative example, white is tinged with blue in thedirection of approx. 150° of θ and with yellow in the direction ofapprox. 45° of θ.

However, the embodiment of the present invention makes it possible tocompletely homogenize the white color tone in a range up to ±50° of φ inevery direction and improve the homogeneity to a viewing angledirection.

As described above, the embodiment 8 of the present invention makes itpossible to improve the homogeneity of color tone, tone reversal, andcontrast ratio to a viewing angle and obtain a liquid crystal displaydevice with wide viewing angle characteristics closer to those of acathode ray tube.

[Embodiment 9]

The embodiment 9 of the present invention is the same as the embodiment8 except the values of φLC1, φLC2, φP1, and φP2.

In the case of the embodiment 9 of the present invention, φLC1 is set to87.5°, φLC2 is set to 92.5°, φP1 is set to 90°, and φP2 is set to 0°.

Similarly to the embodiment 8, rotation angles of liquid crystalmolecules in two rubbing regions are thereby symmetric with respect to aline normal to the direction (EDR) of an electric field.

Therefore, the effect for offsetting coloring each other is furtherimproved and an angle range in which the white color tone is constantcan further be expanded.

Moreover, tone reversal and contrast ratio can homogeneously be averagedin every direction.

Furthermore, in the case of the embodiment 8, a problem occurs that thecontrast ratio decreases to about 4 because the angles between initialorientation directions (RDR1, RDR2) and a transmission axis direction(OD1) of a bottom polarizer (POL1) are as large as 15° and thereby,black level does not completely sink when no voltage is applied.

In the case of the structure of the embodiment 9 of the presentinvention, however, because angles formed between initial orientationdirections (RDR1, RDR2) and a transmission axis direction (OD1) of abottom polarizer (POL1) can be set to a value close to 0°, black levelcompletely sinks when no voltage is applied, the contrast ratio can beimproved, and a contrast ratio about 100 can be achieved for theembodiment 9 of the present invention.

In the case of the embodiment of the present invention, LC1 is set to88.5° and φLC2 is set to 92.5°. However, when these values are closer to90°, it is possible to further improve the contrast ratio.

Moreover, in the case of the embodiment of the present invention, φLC1is set to 177.5° and φLC2 is set to 2.5° when liquid crystal withnegative dielectric anisotropy is used.

[Embodiment 10]

The embodiment of the present invention is the same as the aboveembodiment 8 except φP1 and φP2.

In the embodiment 10 of the present invention, φLC1 is set to 45°, φLC2is set to 135°, φP1 is set to 90° and φP2 is set to 0°.

Thereby, two initial orientation directions RDR1 and RDR2 are bothtilted to −45° and 45° from a transmission axis direction OD1, and showthe maximum transmittance when no voltage is applied.

Moreover, when a voltage is applied, major axes (optical axes) of liquidcrystal molecules in each region rotate up to −45° or 45° to thedirection of applied voltage and coincides with a transmission axisdirection OD2 to obtain a black image.

That is, the normally white mode can be obtained.

In the embodiment 10 of the present invention, liquid crystal moleculesin every region between electrodes are finally lined up in the direction(EDR) of the applied electric field, and it is possible to make majoraxes of liquid crystal molecules completely parallel with thepolarized-light transmission axis OD2 of one polarizing plate.

Therefore, a preferable black level can be displayed and the contrastratio becomes the same level or larger than that of the above embodiment9.

As a result, the embodiment 10 of the present invention makes itpossible to obtain a contrast of 120.

In the embodiment 10 of the present invention, though the liquid crystalmolecules are arranged in one direction (0°) when an electric field isapplied, the problem of coloring is hardly recognized because thecoloring occurs in displaying dark images.

As described above, the embodiment 10 of the present invention makes itpossible to obtain the same effect as the above embodiment 9.

Moreover, the embodiment 10 of the present invention makes it possibleto perform brighter white display because white display is performedwhen no voltage is applied, and thereby, a homogeneous transmittance canbe obtained in a region between electrodes.

[Embodiment 11]

The embodiment 11 of the present invention is the same as the aboveembodiment 10 except the following structure.

FIG. 24 is a top view showing one pixel and its neighborhood of theactive-matrix color liquid crystal display device of the embodiment 11.

The embodiment 11 of the present invention is different from theembodiment 8 in FIG. 23 only in the way of arranging two regions withdifferent rubbing directions.

When a rubbing boundary is set as shown in FIG. 23, an imperfectorientation region (domain) is formed nearby the boundary, and, thereby,the contrast ratio decreases and the image quality deteriorates.

Therefore, in the case of the embodiment 11 of the present invention,the boundary between two regions 501 and 502 with different rubbingdirections is set over a pixel electrode.

It is also possible to set the boundary between two regions 501 and 502with different rubbing directions over a counter electrode.

Thereby, because the region where a domain is produced can be formedover a metallic electrode unrelated to an image display region, it ispossible to prevent deterioration of display quality and decrease ofcontrast ratio due to the domain. Therefore, in the case of theembodiment 11 of the present invention, a contrast ratio of 200 and moreexcellent display quality can be obtained.

As described above, the embodiment 11 of the present invention makes itpossible to obtain a very-high-image-quality liquid crystal displaydevice.

[Embodiment 12]

The embodiment 12 of the present invention is the same as embodiment 8except the following structure.

Each of the above embodiments 8 to 11 controls initial orientationdirections (φLC1 and φLC2) by rubbing top orientation film (ORI1) andbottom orientation film (OR12).

However, by rubbings twice, it is necessary to mask one of two regionsin one picture element so that the other region is not rubbed.

Therefore, the number of steps of applying and removing resist formasking increases and thereby, the throughput decreases or the directmaterial cost increases.

Therefore, the embodiment 12 of the present invention is constituted sothat it is enough to rub only either of top and bottom orientation films(ORI1 and ORI2).

In the embodiment 12 of the present invention, parallel orientationcontrol power is provided for liquid crystal molecules by adding chiralagents for clockwise spin and counterclockwise spin to liquid crystalcomposition of liquid crystal layer (LC) at a ratio of approx. 50% :50%.

Thereby, when an initial orientation direction RDR at a side of oneorientation film is determined, an initial orientation direction RDR atthe side of the other orientation film is naturally determined.

Therefore, it is enough to rub only one orientation film, the number ofsteps of applying and removing resist for masking can be halved, anddecrease of the throughput and increase of the direct material cost canbe prevented.

Moreover, the embodiment 12 of the present invention can be applied toeach of the above embodiments and advantages of each embodiment can bereproduced.

As described above, the embodiment of the present invention not only hasthe advantages of embodiment 8 but also makes it possible to halve thenumber of steps of applying and removing resist required for rubbing andprevent the throughput from decreasing and the direct material cost fromincreasing.

[Embodiment 13]

The embodiment 13 of the present invention is the same as the aboveembodiment 8 except the following structure.

Each of the above embodiments 1 to 12 controls initial orientationdirections φLC1 and φLC2) of liquid crystal molecules by rubbing eitheror both of top orientation film (ORI1) and bottom orientation film(OR12).

FIG. 26 is an 1 Illustration showing a method for applying a laser beamhaving two predetermined polarized directions to different regions of abottom orientation film (ORI1) of the active-matrix color liquid crystaldisplay device which is embodiment 13 of the present invention.

The embodiment 13 of the present invention applies two polarizationlaser beams (L1 and L2) with two different polarization directions totwo regions whose initial orientation directions should be changed.

Because an interface control power or a so-called anchoring powerbetween polyimide or urethane used, as orientation film (ORI) and liquidcrystal molecules changes in accordance with the polarization directionof the light, liquid crystal molecules are initial-oriented in thepolarization direction of a laser beam.

Therefore, it is possible to initially orient liquid crystal moleculesfacing orientation film (ORI) in one picture element to two directionswithout applying resist.

Moreover, the embodiment 13 of the present invention can be applied toeach of the above embodiments and advantages of each embodiment can bereproduced.

As described above, the embodiment 13 of the present invention not onlyhas the advantages of embodiment 8 but also makes it possible todecrease the number of steps of applying and removing resist requiredfor rubbing and prevent the throughput from decreasing and the directmaterial cost from increasing.

The present invention is described in detail in accordance withembodiments.

However, the present invention is not restricted to the embodiments. Itis needless to say that various modifications of the present inventionare permitted as long as they follow the gist of the present invention.

Advantages obtained from a typical invention among those disclosed inthis application are briefly described below.

(1) The present invention makes it possible to offset color tone shiftseach other and greatly reduce the dependency of white color tone onviewing angles in an active-matrix liquid crystal display device usingan in-plane field type.

Moreover, characteristic of the minor axis direction of liquid crystalmolecules hardly causing tone reversal and that of the major axisdirection of liquid crystal molecules easily causing tone reversal areaveraged and a no tone reversal viewing angle range can be expanded.

(2) The present invention makes it possible to lower the driving voltageand increase the response speed by arranging the driving direction ofliquid crystal molecules between a pair of driving electrodes into asingle direction.

(3) The present invention makes it possible to provide a very highquality liquid crystal display device capable of realizing viewing anglecharacteristics equal to those of a CRT.

1. A liquid crystal display device comprising: a first substrate; asecond substrate; a liquid crystal layer sandwiched between the firstand second substrates; and an orientation film formed on the firstsubstrate; wherein the orientation film has two orientation regions in apixel, and the orientation regions are formed by polarized light.
 2. Theliquid crystal display device according to claim 1, wherein the liquidcrystal layer is negative dielectric anisotropy.
 3. The liquid crystaldisplay device according to claim 2, wherein an initial orientation isdifferent between the two orientation regions.
 4. The liquid crystaldisplay device according to claim 3, wherein the two orientation regionsinclude a top region and a bottom region in a pixel.
 5. The liquidcrystal display device according to claim 4, wherein the two orientationregion include a left region and a right region in a pixel.
 6. Theliquid crystal display device according to claim 5, wherein thepolarized light is a polarization light beam.
 7. The liquid crystaldisplay distance according to claim 6, wherein the polarization lightbeam is a laser beam.
 8. The display device according to claim 3,wherein a distance between a first connector and one of two connectingportions and a distance between a second connector and another of thetwo connecting portions is different.
 9. A process for making a liquidcrystal display device including the steps of: forming an orientationfilm on a substrate; radiating a first polarized light in a first regionin a pixel; radiating a second polarized light in a second region in thepixel; and forming a liquid crystal layer on the film.
 10. The processfor making a liquid crystal display according to claim 9, wherein theliquid crystal layer has a negative dielectric anisotropy.
 11. Theprocess for making a liquid crystal display according to claim 10,wherein at least one of the first and second polarized lights is apolarized light beam.
 12. The process for making a liquid crystaldisplay according to claim 11, wherein the polarized light beam is laserbeams.